Insights into self-discharge processes of Al-graphite batteries

Abstract

Aluminum graphite dual ion batteries (AGDIB) have been widely explored thanks to abundant electrode materials, a long cycle life and high power density. However, the shelf life of AGDIBs is so far barely understood. This work's detailed self-discharge investigations allow the quantification of capacity losses for up to 4 weeks, confirm a deintercalation mechanism by Raman spectroscopy and X-ray diffraction, and furthermore allow insights into influence factors. While a cell employing typical materials such as a natural graphite cathode, Mo current collector and AlCl3/[EMIm]Cl=1.5 ionic liquid electrolyte exhibits a capacity loss of 10 % in 24 h, this value can be significantly reduced to 3 % in 24 h when using a glassy carbon current collector and AlCl3/Et3NHCl=1.5 electrolyte instead. Iron impurities within the electrolyte do not affect battery capacities or self-discharge, since it is deposited on the Al anode within the battery soon after assembly. In general, the instability of the current collector material, gas evolution due to electrolyte oxidation at high cell potentials, and cationic electrolyte species greatly influence the self-discharge independently. Electrolyte speciation changes directly related to self-discharge processes are revealed by IR spectroscopy.